The present invention relates generally to cooling systems for electronics packages and, in particular, to an apparatus for cooling electronic components in a phase change electronic cooling system.
Electronic components, such as field effect transistors (FETs) and other types of transistors, generate large amounts of heat in operation and need to be cooled in order to operate at peak efficiency. Numerous types of cooling systems are utilized to cool electronics, including electric fans for ventilating electronic device housings and air conditioning units for those electronic components located in enclosed rooms. Phase change electronic cooling systems, so named because they utilize the heat generated from electronic components to change a liquid coolant to a vapor state to cool the electronic equipment, are also well known. The latent heat of vaporization, for most liquids, is quite substantial, and thus provides an ideal means for absorbing heat from a heat source. In addition, phase change cooling systems offer the ability to reduce packaging space and provide the most efficient electronic component cooling. A typical phase change electronic cooling system is a closed cycle system where the electronic components are placed in a sealed container and immersed in a nonconductive liquid including, but not limited to, Fluorinert(copyright) liquid, manufactured by the 3M Corporation. As the liquid absorbs heat from the electronic components, the liquid boils, turning into a vapor state in a space above the surface of the liquid. The vapor then transfers its heat to a heat exchanger, typically located at the top of the sealed container, and in the process is converted back to a liquid, returning to the liquid in the bottom of the container, where the closed cycle begins again. This type of cooling system is very efficient when the electronics remain immersed in the liquid but the system is dependent on the electronics to be immersed in the liquid for cooling, because the vapor cannot readily absorb any more heat in that state.
When an electronics package with a phase change cooling system is mounted in an automotive vehicle, however, there is a tendency for the electronic components to be exposed to the vapor as the vehicle encounters hills or performs dynamic maneuvers because as the vehicle moves away from the normal horizontal orientation, the liquid tends not to stay level or splashes about. This is disadvantageous because when the electronic components are surrounded only by vapor, and not coolant. The prior art has recognized this problem and has attempted to rectify the problem by providing phase change cooling systems that include a pump that provides pressurized nonconductive liquid to conduits adjacent to the electronic components surrounded by vapor. This type of cooling system, however, is disadvantageous because of the high cost of the pumps, the prime mover, and the piping, relative to the cost of the electronics and the sealed container. In addition, the cooling system operation is dependent on the operation of the pump.
It is desirable, therefore, to provide a cost-effective and efficient means for cooling electronic components in a phase change electronic cooling system regardless of the orientation of the electronic components or the vehicle operating mode.
The present invention concerns a passive cooling system for electronic components in a phase change cooling system. The cooling system includes electronic components located in a sealed container partially filled with a nonconductive liquid. The liquid is preferably Fluorinert(copyright) liquid, manufactured by the 3M Corporation, or another similar nonconductive liquid. The electronic components are immersed in the liquid when the container is in a predetermined orientation relative to the ground. The present invention also includes a hood, located above the high heat generating electronic components near the bottom of the sealed container. Attached to the hood is one end of at least one tube that will allow the vaporized coolant generated from cooling the components to be directed into the tube. The upward motion of the vapor forms bubbles and carries the bubbles and entrained nonconductive liquid into the one end and up the tube. An opposite end of the at least one tube is located adjacent to a portion of the electronics. A heat exchanger, in fluid communication with a fluid transfer system, is located at an upper portion of the sealed container. In operation, the electronics transfer heat to the nonconductive liquid, which vaporizes and forms vapor bubbles. The vapor bubbles rise to the upper portion of the sealed container, are condensed by the heat exchanger, return to the liquid level, and the cycle repeats.
The opposite end of the at least one tube is also located in a manner that directs the coolant and vapor flow to the electronic components that are exposed only to coolant vapors when climbing hills or during dynamic vehicle maneuvers. When the container is oriented to expose a portion of the electronic components above the liquid level, the bubbles and the entrained liquid exit the opposite end of the at least one tube onto the exposed portion of the electronic components to cool the exposed portion of the electronic components.
The present invention advantageously allows for continuous contact of the liquid form of the phase change coolant with the electronic components regardless of the orientation or dynamic inputs to the electronics. The tubes are used like a hose or fountain to assure adequate cooling of all the electronic components in the container in all vehicle operating modes.